1. Field of the Invention
The present invention relates to an SBAS navigation data update notifying system and method used in a ground based augmentation system (GBAS), which can improve the safety by avoiding deterioration in a positioning accuracy caused because SBAS data used in a ground system and in an airborne system which configure the GBAS are different.
2. Description of the Related Art
There have been conducted operations of systems which use four or more navigation satellites for navigations of flying objects such as airplanes (Japanese Unexamined Patent Publication 2000-275317: Patent Document 1, Japanese Unexamined Patent Publication 2003-18061: Patent Document 2, Japanese Unexamined Patent Publication 5-234000: Patent Document 3, and Japanese Unexamined Patent Publication 2004-198291: Patent Document 4).
When the flying objects are airplanes, high safety and reliability are required. In order to meet such demands, it is necessary to satisfy the accuracy, absoluteness, and continuity as well as the availability of the service. However, the four factors cannot be satisfied with a navigation system which uses only a GPS satellite but uses no augmentation system. Therefore, it is necessary to have an augmentation system.
A ground based augmentation system (GBAS) has been proposed as such augmentation system. The GBAS is configured with a ground system, an airborne system, and navigation satellites (GPS satellite and SBAS satellite). The ground system collects data from the navigation satellites by a plurality of reference stations placed within an airport, estimates an error contained in ranging signals from the navigation satellites, and transmits it to the airborne system. The airborne system uses correction data received from the ground system to correct the ranging signals received at the airborne system so as to conduct differential positioning, calculates the displacement from a regulated flight path, and provides it to pilots.
GBAS Type 1 data specification is depicted in SARPs Annex 10 (International Standards and Recommended Practices: referred to as SARPs hereinafter). Note here that SARPs Annex 10 is the International Standards regarding radio navigation devices issued by ICAO (International Civil Aviation Organization). When the GBAS Type 1 generated by a standard designing method based on the specification is used, it is not possible for the airborne system side to know the GBAS navigation data that is used when the ground system generates the GBAS type 1 data.
Therefore, at the timing where the SBAS navigation data is updated, the airborne system comes to use the SBAS navigation data that is different from the one used by the ground system when generating the GBAS type 1 data. The SBAS navigation data is the data used for calculating the satellite position of the SBAS satellite and time correction amount. Thus, use of different data in the ground system and in the airborne system leads to deteriorating the positioning accuracy. The GBAS is a system used in navigations of the airplanes, so that deterioration of the positioning accuracy may endanger people's lives. Therefore, it is necessary to avoid such case.
In order to perform the differential correction with high precision, it is necessary for the SBAS navigation data used by the ground system when generating the correction data to be the same as the SBAS navigation data used by the airborne system for the positioning.
In the GBAS Type 1 data transmitted from the ground system to the airborne system, there are fields such as a field for storing correction data for the ranging signal, a field for storing information regarding absoluteness, and an IOD field for specifying the navigation data used when the ground system generates the correction data.
It is so regulated in the regulation of the SARPs that IODE within the GPS navigation data is set in the IOD field when the correction-target satellite is the GPS satellite. With this, the airborne system can specify the GPS navigation data used by the ground system. Meanwhile, it is so defined in the SARPs that 1 (1111 1111) is set for all the IOD fields when the correction-target satellite is the SBAS satellite. Therefore, when the correction-target satellite is the SBAS satellite, the airborne system cannot specify the SBAS navigation data that is used by the ground system.
For solving the above-described problems, it is considered to apply a navigation system described in Patent Document 1.
Patent Document 1 is directed to a wide-range positioning system which employs a GPS navigation system that uses only a GPS satellite. Patent Document 2 discloses a technique which transmits correction data towards an airplane from a ground system via a stationary satellite, and the airplane receives the correction data and determines the position of the airplane itself accurately.
As described above, Patent Document 1 discloses the system which uses only the GPS satellite, so that the target satellite that receives information is limited to the GPS satellite. Thus, it is not the technique which controls the navigation by using different types of systems as proposed in the present invention, so that it is unnecessary in that case to monitor the update of the navigation data of the SBAS satellite. Therefore, with Patent Document 1, it is not necessary to notify the airborne system that the SBAS navigation data has been updated by adding such information to the correction data transmitted from the ground system.
Thus, there is no necessity to apply the technique of Patent Document 1 to the GBAS system that is configured with the GBAS ground system and the GBAS airborne system.